1. Field of the Invention
This invention relates to a wire-dot printer and, more particularly, to an apparatus for and method of driving a printing head of such a wire-dot printer including actuating devices for driving dot-impact wires or rods, the actuating devices each comprising an electroexpansive element which is expanded and shrunk, respectively, by electrically charging and discharging same.
2. Description of the Related Art
Recently, high-speed wire-dot printing heads have become more widely used, and accordingly, to drive the dot-impact wires of such a high-speed printing head, actuating means comprising electroexpansive elements have been developed and used instead of the usual electromagnetic type driving elements.
For example, U.S. Pat. No. 4,435,666 and page 92 of a publication "NIKKEI (Japan Economic) MECHANICAL" issued on Mar. 12, 1984, suggest that a printing head including such electroexpansive elements can be used. This electroexpansive element is made by following the steps of preparing a plurality of green sheets made of piezo-electric ceramics, forming a metal paste film on one of the surfaces of each of the green sheets thereby to form an inner electrode, and laminating and sintering the plurality of green sheets.
To make a printing head using such an actuating device, the provision of means for effectively enlarging the very small physical, or mechanical, displacement produced by the expansion and shrinking of such an electroexpansive element is essential. Further, very sophisticated drive means are necessary to meet the requirements for high speed wire-dot printing.